This invention relates in general to light fixtures and, more specifically, to air-cooled light fixtures adapted to emit a narrow spectral energy band.
Many optical devices include a light source and an adjacent optical system adapted to direct light in a desired direction. Typical of these are slide or motion picture projector in which a light-and-shadow or colored transparency is positioned in the optical path, stage lighting in which colored filters are interposed to provide a selected color of projected light, infrared sources in which filters in the optical path absorb all but infrared radiation and the like. A problem common to all of these systems is overheating by absorption of heat in the structure, filters, optical system, etc. The transparencies or filters are inherently heated, since all energy except in the spectral band transmitted must be absorbed. A variety of devices and systems have been designed to remove this excess heat to prevent thermal damage to system components and to permit more convenient handling and use of the light fixture. For example, excess heat in stage lighting is very uncomfortable for performers and may damage filters used to select light of different colors.
Most film projectors utilize a fan and conduits to direct a stream of air past the film gate, perpendicular to the optical axis. Typical of these arrangements are those shown in U.S. Pat. Nos. 2,395,561; 3,338,132 and 1,966,531. While generally effective in protecting the film, these systems are large and cumbersome, requiring fans and conduits outside the optical path to provide and direct the air stream. While these cool the film they are less effective in cooling the optical components and light source, which may be damaged by overheating and allow considerable heat to be emitted with the projection light.
Attempts have been made to cool optical systems by liquids circulated between a heat exchanger and the lens housing, by passing air between lens elements perpendicular to the optical axis (as described, for example, in U.S. Pat. No. 2,080,120) and the like. These arrangements are not fully effective, since sufficient heat transfer between the fluid and the optical elements is not always possible and fluid manifolds, conduits, pumps or fans, heat exchangers, etc., are required adjacent to the optical path, producing a wide, heavy and bulky assembly.
Thus, there is a continuing need for a light fixture having an effective means for removing heat from optical elements, such as filters, the housing and the energy source which is simple, light-weight, and sufficiently cool for easy handling and operation.